ethnic group of China. Originally, the Hakka were North Chinese, but they migrated to South China (especially Guangdong, Fujian, Jiangxi, and Guangxi provinces) during the fall of the Nan (Southern) Song dynasty in the 1270s. Worldwide they are thought to number about 80 million today, although the number of Hakka speakers is considerably lower. They are considered to be a branch of the Han....

river, Middle East. The longest river in Southwest Asia, it is one of the two main constituents of the Tigris-Euphrates river system. The river rises in Turkey and flows southeast across Syria and through Iraq. Formed by the confluence of the Karasu and the Murat rivers in the high Armenian plateau, the Euphrates descends between major ranges of the Taurus Mountains...

Sculptors such as Mariano Benlliure (from Spain) and Humberto Peraza (from Mexico) have also been drawn to bullfighting themes. A superb example of Benlliure’s work can be seen in the graveyard at Sevilla where, depicted in bronze, are 12 life-size figures carrying the open coffin of the great Joselito, who was killed by a bull in 1920. Peraza’s enormous bronze bulls and matadors can...

...and producing an Indonesian-language magazine before he was arrested by the Dutch authorities in 1947. He wrote his first published novel, Perburuan (1950; The Fugitive), during a two-year term in a Dutch prison camp (1947–49). That work describes the flight of an anti-Japanese rebel back to his home in Java....

either of two species of fish, the common and the yellow perch (Perca fluviatilis and P. flavescens, sometimes considered as single species, P. fluviatilis) of the family Percidae (order Perciformes). The name also is widely, and sometimes confusingly, applied to a variety of other fishes....

During the 1980s and ’90s a series of experiments demonstrated trophic cascades by adding or removing top carnivores, such as bass (Micropterus) and yellow perch (Perca flavescens), to or from freshwater lakes. Those experiments showed that trophic cascades controlled biomass and production of phytoplankton, recycling rates of nutrients, the ratio of nitrogen to phosphorus......

...(genus Cytomegalovirus). Members of subfamily Gammaherpesvirinae, which is composed of the genera Lymphocryptovirus, Macavirus, Percavirus, and Rhadinovirus, include Epstein-Barr virus, baboon, orangutan, and gorilla herpesviruses, and herpesvirus saimiri. The replication rate of gammaherpesviruses is......

city, Gaspésie–Îles-de-la-Madeleine region, eastern Quebec province, Canada. It lies along the Gulf of St. Lawrence at the east end of the Gaspé Peninsula. First visited in 1534 by Jacques Cartier, it has been the site of a Roman Catholic mission since 1670. Percé is no...

Some illusions are related to characteristics of the perceiver, namely the functioning of the brain and the senses, rather than to physical phenomena that distort a stimulus. Many common visual illusions are perceptual: they result from the brain’s processing of ambiguous or unusual visual information. Other illusions result from the aftereffects of sensory stimulation or from conflicting.....

...was enacted in 1918 to stimulate oil production for World War I (even though the war had just ended). Discovery value proved too hard to estimate, however, so this was changed in 1926 to the “percentage depletion” for oil and gas property, under which the corporation deducts a fixed percentage of its sales as a depletion allowance, regardless of the amount invested. In......

Percentiles provide an indication of how the data values are spread over the interval from the smallest value to the largest value. Approximately p percent of the data values fall below the pth percentile, and roughly 100 − p percent of the data values are above the pth percentile. Percentiles are reported, for example, on most standardized tests. Quartiles......

...Oxford (1935–59), where he was educated, Price taught at Magdalen College (1922–24), Liverpool University (1922–23), and Trinity College (1924–35). His earliest book, Perception (1932), rejected causal theories of perception, while a later publication, Thinking and Experience (1953), revealed the importance of conceptual awareness beyond mere symbolic.....

in humans, the process whereby sensory stimulation is translated into organized experience. That experience, or percept, is the joint product of the stimulation and of the process itself. Relations found between various types of stimulation (e.g., light waves and sound waves) and their associated percepts suggest inferences that can be made about the propertie...

In addition to The Ecological Approach to Visual Perception (1979), Gibson’s most important writings include The Perception of the Visual World (1950) and The Senses Considered as Perceptual Systems (1966). His followers organized the International Society for Ecological Psychology in 1981....

a type of artificial neural network investigated by Frank Rosenblatt, beginning in 1957, at the Cornell Aeronautical Laboratory at Cornell University in Ithaca, New York. Rosenblatt made major contributions to the emerging field of artificial intelligence (AI), both through experimental investigations of the properties of ...

...joined the faculty of the Massachusetts Institute of Technology (MIT), where he taught until 1996, when he became professor emeritus. While at MIT, he cowrote (with Marvin Minsky) Perceptrons: An Introduction to Computational Geometry (1969), a seminal work about artificial intelligence (AI). Papert was also instrumental in the creation of the school’s Artificial...

Finally, infants create perceptual categories by which to organize experience, a category being defined as a representation of the dimensions or qualities shared by a set of similar but not identical events. Infants will treat the different colours of the spectrum, for example, according to the same categories that adults recognize. Thus, they show greater attentiveness when a shade of red......

the tendency of animals and humans to see familiar objects as having standard shape, size, colour, or location regardless of changes in the angle of perspective, distance, or lighting. The impression tends to conform to the object as it is or is assumed to be, rather than to the actual stimulus. Perceptual constancy is responsible for the ability to identify objects under various conditions, which...

process by which the ability of sensory systems to respond to stimuli is improved through experience. Perceptual learning occurs through sensory interaction with the environment as well as through practice in performing specific sensory tasks. The changes that take place in sensory and perceptual systems as a result of perceptual learning occur at the levels of behaviour and physiology. Examples o...

...that successfully takes one prey type may then concentrate its search on others of this type and hence may overlook differently coloured prey of the same species. The phenomenon—known as a perceptual set or a search image—is exemplified by the predator of the European snail Cepaea. Predators encounter one morph and form a search image; they continue to hunt for that one......

Perceptual space is the view of things at a particular time and from a fixed position. This is the stationary window view recorded by the camera and represented in the later periods of ancient Greek and Roman paintings and in most Western schools of painting since the Renaissance. Illusions of perceptual space are generally created by use of the linear perspectival system, based on the......

The most pervasive differences in human performance on psychomotor apparatus are associated with chronological age. Scores obtained from nearly all the devices mentioned above are sensitive to age differences. Researchers generally report a rapid increase in psychomotor proficiency from about the age of five years to the end of the second decade, followed by a few years of relative stability......

hero of Arthurian romance, distinguished by his quality of childlike (often uncouth) innocence, which protected him from worldly temptation and set him apart from other knights in Arthur’s fellowship. This quality also links his story with the primitive folktale theme of a great fool or simple hero. In Chrétien de Troyes’s poem Le Conte du Graal (12t...

either of two species of fish, the common and the yellow perch (Perca fluviatilis and P. flavescens, sometimes considered as single species, P. fluviatilis) of the family Percidae (order Perciformes). The name also is widely, and sometimes confusingly, applied to a variety of other fishes....

old English measure of distance equal to 16.5 feet (5.029 metres), with variations from 9 to 28 feet (2.743 to 8.534 metres) also being used. It was also called a perch or pole. The word rod derives from Old English rodd and is akin to Old Norse rudda (“club”). Etymologically rod is also akin to the Dutch rood which re...

region of northern France on the border of Normandy, mainly in the east of the Orne département, with extensions into neighbouring départements. Formerly a county, it was united with the French crown in 1525. It is largely hilly country, the Perche Hills having summits of...

boulder balanced on a pinnacle rock, another boulder, or in some other precarious position. Some perched rocks form in place, as where rainwash (and in some cases wind) has removed fine material from around the boulder. Others may be transported by tectonic forces (involved in deformation of the Earth’s crust) or by ice (such as erratics, or glacier transports) and let down to an unsettled ...

heavy draft-horse breed that originated in the Perche region of France. The breed probably stems from the Flemish “great horse” of the Middle Ages; modified by Arabian blood to develop a coach-horse type, it was changed again in the 19th century by introduction of draft-type blood to produce animals for heavy farm work. Although a few Percherons ...

any member of the largest order of birds and the dominant avian group on Earth today. The passeriform birds are true perching birds, with four toes, three directed forward and one backward. Considered the most highly evolved of all birds, passerines have undergone an explosive evolutionary radiation in relatively recent geological time and now occur in abundan...

any of the species of the tribe Cairinini, family Anatidae (order Anseriformes), waterfowl that typically inhabit wet woodlands, nest in holes in trees, and perch on branches by means of their long-clawed toes. The tribe is widely represented, especially in the tropics. Perching ducks are closely akin to dabbling ducks, which they resemble in feeding habits and, in some species, courtship behavio...

...later commentaries. Others are sonnets and ballate (ballads), the latter type usually considered his best. One of his best-known ballate was also one of his last, written when he went into exile: “Perch’io non spero di tornar giamai” (“Because I hope not ever to return”), a line that some hear echoed in T.S. Eliot’s refrain from “Ash Wednesday,...

Interest in the chlorates and perchlorates (salts of chloric or perchloric acid) as a base for explosives dates back to 1788. They were mixed with various solid and liquid fuels. Many plants were built in Europe and the United States for the manufacture of this type of explosive, mostly using potassium chlorate, but so far as can be determined, all of them either blew up or burned up, and no......

...central atom increases. For example, because the electronegativity of chlorine (Cl) is greater than that of sulfur (S), which is in turn greater than that of phosphorus (P), it can be predicted that perchloric acid, HClO4, is a stronger acid than sulfuric acid, H2SO4, which should be a stronger acid than phosphoric acid, H3PO4. For a given....

a colourless, dense, nonflammable, highly stable liquid belonging to the family of organic halogen compounds. Tetrachloroethylene is a powerful solvent for many organic substances. By the mid-20th century it had become the most widely used solvent in dry cleaning (displacing carbon tetrachloride and trichloroethylene) and was also commonly used for cleaning metal objects in vapour-degreasing appar...

...popular entertainments derived from them. Similar customs are widespread throughout Europe and extend to the Middle East, India, and parts of Central and South America. Notable examples are the Perchten dancer-masqueraders of Austria, the ritual dances such as the moriscas (or moriscos), santiagos, and matachinas of the Mediterranean and Latin America, and the......

...(and brackish for Nandus) from India to Malaysia. 4 genera, 21 species. West Africa, southern Asia, and the northeast coast of South America. Family Percidae (perches, walleyes, darters)Eocene to present. Spinous and soft dorsal fins usually well separated; anal fin with 1 or 2 spines and.....

pair of French architects and interior designers who carried out many building and decorative projects during the reign of Napoleon I and helped create the influential Empire style of interior decoration....

any member of the largest group of fishes in the world, represented by more than 6,000 species placed in about 150 families. Perciforms are bony fishes that occur in abundance in both marine and freshwater areas of the world, ranging from shallow freshwater ponds to depths of more than 2,300 metres (7,500 feet) in the oceans. Most perciforms are marine fishes,...

any member of the largest group of fishes in the world, represented by more than 6,000 species placed in about 150 families. Perciforms are bony fishes that occur in abundance in both marine and freshwater areas of the world, ranging from shallow freshwater ponds to depths of more than 2,300 metres (7,500 feet) in the oceans. Most perciforms are marine fishes,...

Rare species (Percina tanasi) of darter that originally was found only in the Little Tennessee River in the southeastern U.S. It became the subject of a legal controversy in 1978, when its status as an endangered species delayed for two years the construction of Tellico Dam. The situation was resolved when the fish was successfully introduced into the Hiwassee Ri...

Two species native to East Africa, Kemp’s spiny mouse (A. kempi) and Percival’s spiny mouse (A. percivali), possess the ability to slough off patches of skin when attempting to escape capture from predators. The wounds that remain, which may be painful in appearance, may shrink dramatically within the first 24 hours after the injury. They are covered over by new skin at...

...to at least 200,000 hertz in whales. Bats utilize frequencies from as low as 11,000 hertz (e.g., the European free-tailed bat [Tadarida teniotis]) to as high as 212,000 hertz (e.g., Percival’s trident bat [Cloeotis percivali]). The pulses are repeated at varying rates (often in a single individual, depending upon the situation), beginning at about one per ...

Other prescription drugs came under fire as well in 2009. An FDA panel urged a ban on the popular prescription painkillers Vicodin and Percocet because of their potential for causing liver damage. Those drugs combine acetaminophen with an opiate narcotic. Acetaminophen is an aspirin alternative used in over-the-counter pain relievers, such as Tylenol and Excedrin. High doses of acetaminophen......

...of fishes and crustaceans in all warm seas near shores, especially in tropics; in fresh water. About 3,176 species, some of large size in 73 families.Superfamily Percoidea (basses, perches, sunfishes, and relatives)About 73 families grouped together because they show no great morphological specialization away....

All the features distinguishing the order Perciformes are found in the fishes of the most generalized group, the suborder Percoidei, which contains the sea basses, sunfishes, perches, and fishes of many other families. The order is likely not monophyletic. As the subordinal name implies, the fishes composing it are “percoid,” or perchlike in appearance. The fishes in the other......

...methods of extracting flavour and aroma from ground coffee. In steeping or boiling, pulverized coffee is measured into hot water, which is set or boiled before being poured off the grounds. In percolation, water is brought to the boil in an urn and fed up a tube to a basket holding the coffee. After filtering through the coffee, the water drips back to the urn, where it is forced back up......

...on the texture of the soil (i.e., relative amounts of gravel, sand, silt, and clay). Permeability can be evaluated by direct observation of the soil in excavated test pits and also by conducting a percolation test, or “perc test.” The perc test measures the rate at which water seeps into the soil in small test holes dug on the disposal site. The measured perc rate can be used to.....

Another classification distinguishes the surface zones, or facies, on parts of a glacier. In the dry-snow zone no surface melting occurs, even in summer; in the percolation zone some surface melting may occur, but the meltwater refreezes at a shallow depth; in the soaked zone sufficient melting and refreezing take place to raise the whole winter snow layer to the melting temperature, permitting......

semisynthetic drug with potent pain-relieving effects that is derived from thebaine, an alkaloid that occurs naturally in the opium poppy (Papaver somniferum). Oxycodone was synthesized from thebaine in 1916 and was first used clinically the following year. Today it is prescribed for moderate to severe pain and is sold under ...

...Series. 1 family, Mugilidae, with about 17 genera and as many as 80 species. Coastal marine and brackish or freshwater; tropical and temperate seas.Series Percomorpha (perches and perchlike fishes)Pelvic fin with 1 spine and 5 rays (or number of rays reduced); pelvic fin connected to ...

...marine; bottom dwellers, coasts of South America, South Africa, Indo-Pacific to Japan; a few good food species.Family Percophidae (duckbills)Forms resemble flatheads of family Platycephalidae; body long, slender; head flattened; eyes on top of head, close together; separate spinous and soft dorsal...

...order that encompasses the codfishes, contains about 555 species. About 210 species are contained within the order Lophiiformes, which is made up of the anglerfishes. There are about 9 species of percopsiforms, or trout-perches, and about 385 species of ophidiiforms (that is, the pearlfishes and cusk-eels)....

either of two species of small, dark-spotted fishes of the genus Percopsis (family Percopsidae), found in freshwaters of North America. The larger species, P. omiscomaycus, grows about 15 cm (6 inches) long and is found in central North America. The second, P. transmontana, is about 10 cm long and lives in the Columbia River system. Trout-perch are notable in being structural...

in medicine, diagnostic procedure that entails striking the body directly or indirectly with short, sharp taps of a finger or, rarely, a hammer. The procedure was first described in 1761 by the Austrian physician Leopold Auenbrugger von Auenbrugg. Although generally ignored by his contemporaries, it is now routinely employed. The sounds produced by the procedure are helpful in ...

...version of his opera Tannhäuser (1861); 14 years later Georges Bizet employed them with great effect in his opera Carmen. Now, modern rhythm bands frequently include one or two single castanets or a pair attached to a long handle for ease in clicking....

...clappers, concussion stones, castanets, and cymbals. Percussion idiophones, instruments struck by a nonsonorous striker, form a large subgroup, including triangles and simple percussion sticks; percussion beams, such as the semanterion; percussion disks and plaques, single and in sets; xylophones, lithophones (sonorous stones), and metallophones (sets......

...both ends; when plunged in and out of water, it is said to emit the sounds “uh-ah-uh-ah.” Split-bamboo percussion tubes, doubling as rattles, are indigenous to the same area, while the percussion board o-le-polotu of Samoan and Tongan chiefs accompanies solo songs. Slit drums can be huge. Made from a tree trunk, living slit drums in Vanuatu ar...

By the 1860s, percussion caps, which detonate upon being struck a sharp blow by the firing pin of a gun, had been incorporated into a metal cartridge case containing all the components for a complete round that could be used in breech-loading rifles. In the 1880s, the introduction of nitrocellulose, or guncotton, in place of black powder as the propellant charge provided the final element for......

The physics of percussive tools takes into consideration the centre of gravity and what is technically called the centre of percussion—i.e., a unique point associated with a rotation, in this case the arc through which the tool is swung before delivering its blow and coming to rest. The tool’s centre of gravity is readily found because it is the balance point, or location along the h...

Percussive drilling is slower than rotary drilling but has a number of special applications, such as for shallow holes. In percussive drilling, blows are applied successively to a tool attached to rods or a cable, and the tool is rotated so that a new portion of the face is attacked at each blow....

Percussive drilling is slower than rotary drilling but has a number of special applications, such as for shallow holes. In percussive drilling, blows are applied successively to a tool attached to rods or a cable, and the tool is rotated so that a new portion of the face is attacked at each blow....

any musical instrument belonging to either of two groups, idiophones or membranophones. Idiophones are instruments whose own substance vibrates to produce sound (as opposed to the strings of a guitar or the air column of a flute); examples include bells, clappers, and rattles. Membranophones emit sound by the vibration of a stretched membrane; the prime exampl...

in firearms, ignition system of small arms that utilizes an explosive that detonates when sharply struck. Discovered in 1805 by Alexander Forsyth (1786–1843), the percussion lock revolutionized firearms theory and opened the way to the development of self-contained metal cartridges and contact fuses in artillery shells. Forsyth found that potassium chlorate would explode ...

Several tools involve a violent propulsion to deliver a telling blow. These have been named percussive tools, and their principal representatives are the ax and hammer. Under these two names are found an immense number of variations. The percussive group may also be called dynamic because of the swift motion and the large, short-term forces they develop. This means that mass and velocity and,......

...Various techniques that combine contrast agents (dyes) with X-ray imaging are also used to determine whether the bile duct or other ducts within the pancreas are blocked. One example is called percutaneous transhepatic cholangiography (PTC), in which a needle is used to inject a dye directly into the liver, followed by X-ray imaging. Other X-ray imaging techniques include angiography, in......

When coronary arteriography reveals relatively isolated, incompletely obstructive lesions, there are two alternative treatments—medication or coronary angioplasty (balloon dilation of the localized obstruction by a special catheter). When coronary arteriography reveals a severe blockage of the left main coronary artery or proximally in one or more of the major arteries, coronary artery......

Both percutaneous umbilical blood sampling (PUBS) and preimplantation testing are rare, relatively high-risk, and performed only in very unusual cases. Preimplantation testing of embryos derived by in vitro fertilization is a particularly new technique and is currently used only in cases of couples who are at high risk for having a fetus affected with a given familial genetic disorder and who......

Both percutaneous umbilical blood sampling (PUBS) and preimplantation testing are rare, relatively high-risk, and performed only in very unusual cases. Preimplantation testing of embryos derived by in vitro fertilization is a particularly new technique and is currently used only in cases of couples who are at high risk for having a fetus affected with a given familial genetic disorder and who......

Sept. 27, 1919Pensacola, Fla.Sept. 17, 2011Washington, D.C.American politician who was a moderate Republican who served (1967–84) as a U.S. senator from Illinois for three terms and entered the national spotlight after proposing in May 1973 that an independent prosecutor investigate ...

...folk songs, ballads, and others form a lively body of compositions. Oral transmission was probably common, and the survival of much of what is extant is fortuitous. The manuscript known as the Percy Folio, a 17th-century antiquarian collection of such material, may be a fair sampling of the repertoire of the late medieval itinerant entertainer. In addition to a number of popular romances......

...ended early nonetheless. While still in command, Smith was seriously injured when his gunpowder bag caught fire from mysterious causes. He sailed back to England in early September. A nobleman named George Percy, the eighth son of an earl, took his place as the colony’s leader....

...is renewing his earlier vow to make a pilgrimage to the Holy Land. He learns that Owen Glendower, the Welsh chieftain, has captured Edmund Mortimer, the earl of March, and that Henry Percy, known as Hotspur, son of the earl of Northumberland, has refused to release his Scottish prisoners until the king has ransomed Mortimer. Henry laments that his own son is not like the fearless Hotspur. As th...

English statesman, leading figure during the reigns of England’s Richard II and Henry IV. He and his son Sir Henry Percy, the celebrated “Hotspur,” are commemorated in William Shakespeare’s play 1 Henry IV....

A descendant of the union of Agnes and Josceline, Henry de Percy (1273–1314) was one of Edward I’s most active agents in the subjugation of Scotland until the success of Robert de Bruce made him withdraw into England. Summoned to Parliament as a baron in the time of Edward I, he later, as one of the lords ordainer, supported the baronial opposition to the personal rule of Edward II.....

British metallurgist. He turned to metallurgy after obtaining a medical degree, and in 1848 he devised a process for extracting silver from its ores, which soon came into widespread use. He improved the Bessemer process for making steel, and he was the first to survey British iron ores. At London’s Metropolitan School of Sciences, he trained a generation of metallurgists....

English rebel who led the most serious of the uprisings against King Henry IV (reigned 1399–1413). His fame rests to a large extent on his inclusion as a major character in William Shakespeare’s Henry IV....

participant in the Gunpowder Plot (1605), which aimed to blow up the Houses of Parliament (Palace of Westminster) during the state opening of Parliament, while James I and his chief ministers met within, in reprisal for increasing oppression of Roman Catholics in England....

The family was founded by William de Percy (c. 1030–96), a follower of William I the Conqueror, who bestowed on him a great fief in Yorkshire and Lincolnshire. His grandson William (d. 1175) was the last of the house in the direct line, leaving two daughters and coheiresses, Maud, who died childless, and Agnes. Agnes de Percy married Josceline de Leuven, and from this marriage......

...Macedonia from about 700 to about 311 bc; under their leadership the Macedonian kingdom was created and gradually gained predominance throughout Greece. From about 700 the founder of the dynasty, Perdiccas I, led the people who called themselves Macedonians eastward from their home on the Haliacmon (modern Aliákmon) River. Aegae (Edessa) became the capital, and by the reign...

Alexander’s son Perdiccas II (reigned c. 450–c. 413) asserted his succession against various brothers and united the Greek cities of Chalcidice in a federation centring on the city of Olynthus. Perdiccas’ son Archelaus (reigned c. 413–399) adopted a strongly philhellenic policy, introducing Greek artists to his new capital at Pella. He strengthened ...

Philip was a son of Amyntas III. In his boyhood he saw the Macedonian kingdom disintegrating while his elder brothers Alexander II and Perdiccas III, who each reigned for a few years, strove unsuccessfully against insubordination of their regional vassal princes, intervention of the strong Greek city Thebes, and invasion by the Illyrians of the northwest frontier....

...all or part of their courses and are so altered by the combined effect of wind and sand as to afford little surface evidence of the rivers that once flowed in them. Still other streams, such as the Perdido, terminate in basins containing salt flats or salt ponds. The canyon bottoms consist mostly of deep beds of coarse alluvial sands and gravels, which act as groundwater reservoirs to......

...too is carried out and reported dead. Having lost everyone important to him and having realized the error of his ways, Leontes is left to his solitary despair. Meanwhile, the baby girl, named Perdita, is brought up by a shepherd and his wife in Polixenes’ kingdom of Bohemia. She appears in Act IV as a young and beautiful shepherdess who has been discovered by Polixenes’ son Floriz...

The typical partridge of Europe is the gray partridge (Perdix perdix), called Hungarian (or hun) partridge in North America, where it was introduced in 1889 (Virginia) and again, much more successfully, in 1908–09 (Alberta). It ranges throughout the British Isles and across Europe to the Caspian region. The gray partridge has a reddish face and tail, gray breast, barred sides, and......